This research is directed at a more precise understanding of photoreceptor membrane turnover. The significance of the work derives from the frequent pathological finding of injury to photoreceptors in hereditary and nutritional diseases, retinal detachment and drug studies which suggest that photoreceptor metabolism is in a delicate balance. One aspect of this is the extensive turnover of photosensitive membrane on which photoreceptor function depends. The anatomical polarity of the photoreceptor makes it possible to define a series of discrete "subprocesses" or events which lead to turnover. Although these can be described operationally, the molecular-cellular mechanisms underlying them are poorly defined. This is a proposal to use high-resolution electron microscopic and fluorescence microscopic techniques coupled with specific ligands in an experimental attempt to analyze specific aspects of turnover. Special attention will be focused on the mechanism of visual pigment delivery to forming discs, the relationship of photosensitive membrane to cytoskeletal structures of the ciliary axoneme and the mechanisms involved in photosensitive membrane detachment and phagocytosis by pigment epithelial cells. Improved insight into these aspects of turnover may lead to a better understanding of pathological processes in photoreceptor degeneration.